[appendix]
[[configuration-metadata]]
== Configuration meta-data
Spring Boot jars are shipped with meta-data files that provide details of all supported
configuration properties. The files are designed to allow IDE developers to offer
contextual help and "`code completion`" as users are working with `application.properties`
or `application.yml` files.

The majority of the meta-data file is generated automatically at compile time by
processing all items annotated with `@ConfigurationProperties`. However, it is possible
to <<configuration-metadata-additional-metadata,write part of the meta-data manually>>
for corner cases or more advanced use cases.



[[configuration-metadata-format]]
=== Meta-data format
Configuration meta-data files are located inside jars under
`META-INF/spring-configuration-metadata.json` They use a simple JSON format with items
categorized under either "`groups`" or "`properties`" and additional values hint
categorized under "hints":

[source,json,indent=0]
----
	{"groups": [
		{
			"name": "server",
			"type": "org.springframework.boot.autoconfigure.web.ServerProperties",
			"sourceType": "org.springframework.boot.autoconfigure.web.ServerProperties"
		},
		{
			"name": "spring.jpa.hibernate",
			"type": "org.springframework.boot.autoconfigure.orm.jpa.JpaProperties$Hibernate",
			"sourceType": "org.springframework.boot.autoconfigure.orm.jpa.JpaProperties",
			"sourceMethod": "getHibernate()"
		}
		...
	],"properties": [
		{
			"name": "server.port",
			"type": "java.lang.Integer",
			"sourceType": "org.springframework.boot.autoconfigure.web.ServerProperties"
		},
		{
			"name": "server.servlet.path",
			"type": "java.lang.String",
			"sourceType": "org.springframework.boot.autoconfigure.web.ServerProperties",
			"defaultValue": "/"
		},
		{
			  "name": "spring.jpa.hibernate.ddl-auto",
			  "type": "java.lang.String",
			  "description": "DDL mode. This is actually a shortcut for the \"hibernate.hbm2ddl.auto\" property.",
			  "sourceType": "org.springframework.boot.autoconfigure.orm.jpa.JpaProperties$Hibernate"
		}
		...
	],"hints": [
		{
			"name": "spring.jpa.hibernate.ddl-auto",
			"values": [
				{
					"value": "none",
					"description": "Disable DDL handling."
				},
				{
					"value": "validate",
					"description": "Validate the schema, make no changes to the database."
				},
				{
					"value": "update",
					"description": "Update the schema if necessary."
				},
				{
					"value": "create",
					"description": "Create the schema and destroy previous data."
				},
				{
					"value": "create-drop",
					"description": "Create and then destroy the schema at the end of the session."
				}
			]
		}
	]}
----

Each "`property`" is a configuration item that the user specifies with a given value.
For example `server.port` and `server.servlet.path` might be specified in
`application.properties` as follows:

[source,properties,indent=0]
----
	server.port=9090
	server.servlet.path=/home
----

The "`groups`" are higher level items that don't themselves specify a value, but instead
provide a contextual grouping for properties. For example the `server.port` and
`server.servlet.path` properties are part of the `server` group.

NOTE: It is not required that every "`property`" has a "`group`", some properties might
just exist in their own right.

Finally, "`hints`" are additional information used to assist the user in configuring a
given property. When configuring the `spring.jpa.hibernate.ddl-auto` property, a tool can
use it to offer some auto-completion help for the `none`, `validate`, `update`, `create`
and `create-drop` values.



[[configuration-metadata-group-attributes]]
==== Group Attributes
The JSON object contained in the `groups` array can contain the following attributes:

[cols="1,1,4"]
|===
|Name | Type |Purpose

|`name`
| String
| The full name of the group. This attribute is mandatory.

|`type`
| String
| The class name of the data type of the group. For example, if the group was based
  on a class annotated with `@ConfigurationProperties` the attribute would contain the
  fully qualified name of that class. If it was based on a `@Bean` method, it would be
  the return type of that method. The attribute may be omitted if the type is not known.

|`description`
| String
| A short description of the group that can be displayed to users. May be omitted if no
  description is available. It is recommended that descriptions are a short paragraphs,
  with the first line providing a concise summary. The last line in the description should
  end with a period (`.`).

|`sourceType`
| String
| The class name of the source that contributed this group. For example, if the group
  was based on a `@Bean` method annotated with `@ConfigurationProperties` this attribute
  would contain the fully qualified name of the `@Configuration` class containing the
  method. The attribute may be omitted if the source type is not known.

|`sourceMethod`
| String
| The full name of the method (include parenthesis and argument types) that contributed
  this group. For example, the name of a `@ConfigurationProperties` annotated `@Bean`
  method.  May be omitted if the source method is not known.
|===



[[configuration-metadata-property-attributes]]
==== Property Attributes
The JSON object contained in the `properties` array can contain the following attributes:

[cols="1,1,4"]
|===
|Name | Type |Purpose

|`name`
| String
| The full name of the property. Names are in lowercase dashed form (e.g.
  `server.servlet.path`). This attribute is mandatory.

|`type`
| String
| The full signature of the data type of the property. For example, `java.lang.String`
  but also a full generic type such as `java.util.Map<java.util.String,acme.MyEnum>`.
  This attribute can be used to guide the user as to the types of values that they can
  enter. For consistency, the type of a primitive is specified using its wrapper
  counterpart, i.e. `boolean` becomes `java.lang.Boolean`. Note that this class may be
  a complex type that gets converted from a String as values are bound. May be omitted
  if the type is not known.

|`description`
| String
| A short description of the group that can be displayed to users. May be omitted if no
  description is available. It is recommended that descriptions are a short paragraphs,
  with the first line providing a concise summary. The last line in the description should
  end with a period (`.`).

|`sourceType`
| String
| The class name of the source that contributed this property. For example, if the
  property was from a class annotated with `@ConfigurationProperties` this attribute
  would contain the fully qualified name of that class. May be omitted if the source type
  is not known.

|`defaultValue`
| Object
| The default value which will be used if the property is not specified. Can also be an
  array of value(s) if the type of the property is an array. May be omitted if the default
  value is not known.

|`deprecation`
| Deprecation
| Specify if the property is deprecated. May be omitted if the field is not deprecated
  or if that information is not known. See below for more details.
|===

The JSON object contained in the `deprecation` attribute of each `properties` element can
contain the following attributes:

[cols="1,1,4"]
|===
|Name | Type |Purpose

|`level`
|String
|The level of deprecation, can be either `warning` (default) or `error`. When a property
 has a `warning` deprecation level it should still be bound in the environment. When it
 has an `error` deprecation level however, the property is no longer managed and will not
 be bound.

|`reason`
|String
|A short description of the reason why the property was deprecated. May be omitted if no
 reason is available. It is recommended that descriptions are a short paragraphs,
 with the first line providing a concise summary. The last line in the description should
 end with a period (`.`).

|`replacement`
|String
|The full name of the property that is _replacing_ this deprecated property. May be omitted
 if there is no replacement for this property.
|===

NOTE: Prior to Spring Boot 1.3, a single `deprecated` boolean attribute can be used
instead of the `deprecation` element. This is still supported in a deprecated fashion and
should no longer be used. If no reason and replacement are available, an empty
`deprecation` object should be set.

Deprecation can also be specified declaratively in code by adding the
`@DeprecatedConfigurationProperty` annotation to the getter exposing the deprecated
property. For instance, let's assume the `app.foo.target` property was confusing and
was renamed to `app.foo.name`

[source,java,indent=0]
----
	@ConfigurationProperties("app.foo")
	public class FooProperties {

		private String name;

		public String getName() { ... }

		public void setName(String name) { ... }

		@DeprecatedConfigurationProperty(replacement = "app.foo.name")
		@Deprecated
		public String getTarget() {
			return getName();
		}

		@Deprecated
		public void setTarget(String target) {
			setName(target);
		}
	}
----

NOTE: There is no way to set a `level` as `warning` is always assumed since code is still
handling the property.

The code above makes sure that the deprecated property still works (delegating
to the `name` property behind the scenes). Once the `getTarget` and `setTarget`
methods can be removed from your public API, the automatic deprecation hint in the
meta-data will go away as well. If you want to keep a hint, adding manual meta-data with
an `error` deprecation level ensures that users are still informed about that property and
is particularly useful when a `replacement` is provided.



[[configuration-metadata-hints-attributes]]
==== Hint Attributes
The JSON object contained in the `hints` array can contain the following attributes:

[cols="1,1,4"]
|===
|Name | Type |Purpose

|`name`
| String
| The full name of the property that this hint refers to. Names are in lowercase dashed
  form (e.g. `server.servlet.path`). If the property refers to a map (e.g.
  `system.contexts`) the hint either applies to the _keys_ of the map (`system.context.keys`)
   or the values (`system.context.values`). This attribute is mandatory.

|`values`
| ValueHint[]
| A list of valid values as defined by the `ValueHint` object (see below). Each entry defines
  the value and may have a description

|`providers`
| ValueProvider[]
| A list of providers as defined by the `ValueProvider` object (see below). Each entry defines
  the name of the provider and its parameters, if any.

|===

The JSON object contained in the `values` attribute of each `hint` element can contain the
following attributes:

[cols="1,1,4"]
|===
|Name | Type |Purpose

|`value`
| Object
| A valid value for the element to which the hint refers to. Can also be an array of value(s)
  if the type of the property is an array. This attribute is mandatory.

|`description`
| String
| A short description of the value that can be displayed to users. May be omitted if no
  description is available. It is recommended that descriptions are a short paragraphs,
  with the first line providing a concise summary. The last line in the description should
  end with a period (`.`).
|===

The JSON object contained in the `providers` attribute of each `hint` element can contain the
following attributes:

[cols="1,1,4"]
|===
|Name | Type |Purpose

|`name`
| String
| The name of the provider to use to offer additional content assistance for the element
  to which the hint refers to.

|`parameters`
| JSON object
| Any additional parameter that the provider supports (check the documentation of the
  provider for more details).
|===



[[configuration-metadata-repeated-items]]
==== Repeated meta-data items
It is perfectly acceptable for "`property`" and "`group`" objects with the same name to
appear multiple times within a meta-data file. For example, you could bind two separate
classes to the same prefix, with each potentially offering overlap of property names.
While this is not supposed to be a frequent scenario, consumers of meta-data should take
care to ensure that they support such scenarios.



[[configuration-metadata-providing-manual-hints]]
=== Providing manual hints
To improve the user experience and further assist the user in configuring a given
property, you can provide additional meta-data that:

1. Describes the list of potential values for a property.
2. Associates a provider to attach a well-defined semantic to a property so that a tool
   can discover the list of potential values based on the project's context.


==== Value hint
The `name` attribute of each hint refers to the `name` of a property. In the initial
example above, we provide 5 values for the `spring.jpa.hibernate.ddl-auto` property:
`none`, `validate`, `update`, `create` and `create-drop`. Each value may have a
description as well.

If your property is of type `Map`, you can provide hints for both the keys and the
values (but not for the map itself). The special `.keys` and `.values` suffixes must
be used to refer to the keys and the values respectively.

Let's assume a `foo.contexts` that maps magic String values to an integer:

[source,java,indent=0]
----
	@ConfigurationProperties("foo")
	public class FooProperties {

		private Map<String,Integer> contexts;
		// getters and setters
	}
----

The magic values are foo and bar for instance. In order to offer additional content
assistance for the keys, you could add the following to
<<configuration-metadata-additional-metadata,the manual meta-data of the module>>:

[source,json,indent=0]
----
	{"hints": [
		{
			"name": "foo.contexts.keys",
			"values": [
				{
					"value": "foo"
				},
				{
					"value": "bar"
				}
			]
		}
	]}
----

NOTE: Of course, you should have an `Enum` for those two values instead. This is by far
the most effective approach to auto-completion if your IDE supports it.



==== Value provider
Providers are a powerful way of attaching semantics to a property. We define in the section
below the official providers that you can use for your own hints. Bare in mind however that
your favorite IDE may implement some of these or none of them. It could eventually provide
its own as well.

NOTE: As this is a new feature, IDE vendors will have to catch up with this new feature.

The table below summarizes the list of supported providers:

[cols="2,4"]
|===
|Name | Description

|`any`
|Permit any additional value to be provided.

|`class-reference`
|Auto-complete the classes available in the project. Usually constrained by a base
 class that is specified via the `target` parameter.

|`handle-as`
|Handle the property as if it was defined by the type defined via the mandatory `target` parameter.

|`logger-name`
|Auto-complete valid logger names. Typically, package and class names available in
 the current project can be auto-completed.

|`spring-bean-reference`
|Auto-complete the available bean names in the current project. Usually constrained
 by a base class that is specified via the `target` parameter.

|`spring-profile-name`
|Auto-complete the available Spring profile names in the project.

|===

TIP: No more than one provider can be active for a given property but you can specify
several providers if they can all manage the property _in some ways_. Make sure to place
the most powerful provider first as the IDE must use the first one in the JSON section it
can handle. If no provider for a given property is supported, no special content
assistance is provided either.



===== Any
The **any** provider permits any additional values to be provided. Regular value
validation based on the property type should be applied if this is supported.

This provider will be typically used if you have a list of values and any extra values
are still to be considered as valid.

The example below offers `on` and `off` as auto-completion values for `system.state`; any
other value is also allowed:

[source,json,indent=0]
----
	{"hints": [
		{
			"name": "system.state",
			"values": [
				{
					"value": "on"
				},
				{
					"value": "off"
				}
			],
			"providers": [
				{
					"name": "any"
				}
			]
		}
	]}
----



===== Class reference
The **class-reference** provider auto-completes classes available in the project. This
provider supports these parameters:

[cols="1,1,2,4"]
|===
|Parameter |Type |Default value |Description

|`target`
|`String` (`Class`)
|_none_
|The fully qualified name of the class that should be assignable to the chosen value.
 Typically used to filter out non candidate classes. Note that this information can
 be provided by the type itself by exposing a class with the appropriate upper bound.

|`concrete`
|`boolean`
|true
|Specify if only concrete classes are to be considered as valid candidates.
|===


The meta-data snippet below corresponds to the standard `server.servlet.jsp.class-name`
property that defines the `JspServlet` class name to use:

[source,json,indent=0]
----
	{"hints": [
		{
			"name": "server.servlet.jsp.class-name",
			"providers": [
				{
					"name": "class-reference",
					"parameters": {
						"target": "javax.servlet.http.HttpServlet"
					}
				}
			]
		}
	]}
----



===== Handle As
The **handle-as** provider allows you to substitute the type of the property to a more
high-level type. This typically happens when the property has a `java.lang.String` type
because you don't want your configuration classes to rely on classes that may not be
on the classpath. This provider supports these parameters:

[cols="1,1,2,4"]
|===
|Parameter |Type |Default value |Description

| **`target`**
| `String` (`Class`)
|_none_
|The fully qualified name of the type to consider for the property. This parameter is mandatory.
|===

The following types can be used:

* Any `java.lang.Enum` that lists the possible values for the property (By all means, try to
  define the property with the `Enum` type instead as no further hint should be required for
  the IDE to auto-complete the values).
* `java.nio.charset.Charset`: auto-completion of charset/encoding values (e.g. `UTF-8`)
* `java.util.Locale`: auto-completion of locales (e.g. `en_US`)
* `org.springframework.util.MimeType`: auto-completion of content type values (e.g. `text/plain`)
* `org.springframework.core.io.Resource`: auto-completion of Spring’s Resource abstraction to
  refer to a file on the filesystem or on the classpath. (e.g. `classpath:/foo.properties`)

NOTE: If multiple values can be provided, use a `Collection` or _Array_ type to teach the IDE
about it.

The meta-data snippet below corresponds to the standard `liquibase.change-log`
property that defines the path to the changelog to use. It is actually used internally as a
`org.springframework.core.io.Resource` but cannot be exposed as such as we need to keep the
original String value to pass it to the Liquibase API.

[source,json,indent=0]
----
	{"hints": [
		{
			"name": "liquibase.change-log",
			"providers": [
				{
					"name": "handle-as",
					"parameters": {
						"target": "org.springframework.core.io.Resource"
					}
				}
			]
		}
	]}
----



===== Logger name
The **logger-name** provider auto-completes valid logger names. Typically, package and
class names available in the current project can be auto-completed. Specific frameworks
may have extra magic logger names that could be supported as well.

Since a logger name can be any arbitrary name, really, this provider should allow any
value but could highlight valid packages and class names that are not available in the
project's classpath.

The meta-data snippet below corresponds to the standard `logging.level` property, keys
are _logger names_ and values correspond to the standard log levels or any custom
level:

[source,json,indent=0]
----
	{"hints": [
		{
			"name": "logging.level.keys",
			"values": [
				{
					"value": "root",
					"description": "Root logger used to assign the default logging level."
				}
			],
			"providers": [
				{
					"name": "logger-name"
				}
			]
		},
		{
			"name": "logging.level.values",
			"values": [
				{
					"value": "trace"
				},
				{
					"value": "debug"
				},
				{
					"value": "info"
				},
				{
					"value": "warn"
				},
				{
					"value": "error"
				},
				{
					"value": "fatal"
				},
				{
					"value": "off"
				}

			],
			"providers": [
				{
					"name": "any"
				}
			]
		}
	]}
----



===== Spring bean reference
The **spring-bean-reference** provider auto-completes the beans that are defined in
the configuration of the current project. This provider supports these parameters:

[cols="1,1,2,4"]
|===
|Parameter |Type |Default value |Description

|`target`
| `String` (`Class`)
|_none_
|The fully qualified name of the bean class that should be assignable to the candidate.
 Typically used to filter out non candidate beans.
|===

The meta-data snippet below corresponds to the standard `spring.jmx.server` property
that defines the name of the `MBeanServer` bean to use:

[source,json,indent=0]
----
	{"hints": [
		{
			"name": "spring.jmx.server",
			"providers": [
				{
					"name": "spring-bean-reference",
					"parameters": {
						"target": "javax.management.MBeanServer"
					}
				}
			]
		}
	]}
----

NOTE: The binder is not aware of the meta-data so if you provide that hint, you
will still need to transform the bean name into an actual Bean reference using
the `ApplicationContext`.



===== Spring profile name
The **spring-profile-name** provider auto-completes the Spring profiles that are
defined in the configuration of the current project.

The meta-data snippet below corresponds to the standard `spring.profiles.active`
property that defines the name of the Spring profile(s) to enable:

[source,json,indent=0]
----
	{"hints": [
		{
			"name": "spring.profiles.active",
			"providers": [
				{
					"name": "spring-profile-name"
				}
			]
		}
	]}
----



[[configuration-metadata-annotation-processor]]
=== Generating your own meta-data using the annotation processor
You can easily generate your own configuration meta-data file from items annotated with
`@ConfigurationProperties` by using the `spring-boot-configuration-processor` jar.
The jar includes a Java annotation processor which is invoked as your project is
compiled. To use the processor, simply include `spring-boot-configuration-processor` as
an optional dependency, for example with Maven you would add:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-configuration-processor</artifactId>
		<optional>true</optional>
	</dependency>
----

With Gradle, you can use the https://github.com/spring-gradle-plugins/propdeps-plugin[propdeps-plugin]
and specify:

[source,groovy,indent=0,subs="verbatim,quotes,attributes"]
----
	dependencies {
		optional "org.springframework.boot:spring-boot-configuration-processor"
	}

	compileJava.dependsOn(processResources)
----

NOTE: You need to add `compileJava.dependsOn(processResources)` to your build to ensure
that resources are processed before code is compiled. Without this directive any
`additional-spring-configuration-metadata.json` files will not be processed.

The processor will pick up both classes and methods that are annotated with
`@ConfigurationProperties`. The Javadoc for field values within configuration classes
will be used to populate the `description` attribute.

NOTE: You should only use simple text with `@ConfigurationProperties` field Javadoc since
they are not processed before being added to the JSON.

Properties are discovered via the presence of standard getters and setters with special
handling for collection types (that will be detected even if only a getter is present). The
annotation processor also supports the use of the `@Data`, `@Getter` and `@Setter` lombok
annotations.

[NOTE]
====
If you are using AspectJ in your project, you need to make sure that the annotation
processor only runs once. There are several ways to do this: with Maven, you can
configure the `maven-apt-plugin` explicitly and add the dependency to the annotation
processor only there. You could also let the AspectJ plugin run all the processing
and disable annotation processing in the `maven-compiler-plugin` configuration:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<plugin>
		<groupId>org.apache.maven.plugins</groupId>
		<artifactId>maven-compiler-plugin</artifactId>
		<configuration>
			<proc>none</proc>
		</configuration>
	</plugin>
----
====



[[configuration-metadata-nested-properties]]
==== Nested properties
The annotation processor will automatically consider inner classes as nested properties.
For example, the following class:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@ConfigurationProperties(prefix="server")
	public class ServerProperties {

		private String name;

		private Host host;

		// ... getter and setters

		private static class Host {

			private String ip;

			private int port;

			// ... getter and setters

		}

	}
----

Will produce meta-data information for `server.name`, `server.host.ip` and
`server.host.port` properties. You can use the `@NestedConfigurationProperty`
annotation on a field to indicate that a regular (non-inner) class should be treated as
if it were nested.



[[configuration-metadata-additional-metadata]]
==== Adding additional meta-data
Spring Boot's configuration file handling is quite flexible; and it is often the case
that properties may exist that are not bound to a `@ConfigurationProperties` bean. You
may also need to tune some attributes of an existing key. To support such cases and allow
you to provide custom "hints", the annotation processor will automatically merge items
from `META-INF/additional-spring-configuration-metadata.json` into the main meta-data
file.

If you refer to a property that has been detected automatically, the description,
default value and deprecation information are overridden if specified. If the manual
property declaration is not identified in the current module, it is added as a brand new
property.

The format of the `additional-spring-configuration-metadata.json` file is exactly the same
as the regular `spring-configuration-metadata.json`. The additional properties file is
optional, if you don't have any additional properties, simply don't add it.
